Aartsy19

Well.. What about me using only 94 octane at sunoco? I have ONLY put 94sunoco in my Mbeast..

Neccessary?

2exclusive

i thought they stopped making 94 octane in sunoco hmmm

pjinca

He's in Canada, they may get "the good stuff" there.

xcntrk

I've dealt extensively with this subject, so I'll add my $0.02

Premium unleaded is required because the north-American based vehicles are tuned for performance based on the octane levels found in premium fuel, also known as the anti-knock index. Premium unleaded in the US contains 91 or 93 octane (depending on region) and therefore allows superior knock prevention over say regular unleaded (87 octane). So the only difference from an equipment standpoint, is that the manufacture can tune for performance more aggressively with premium allowing for more power by pushing ignition-advance or in turbo models, more boost, etc.

When using a lower octane fuel in a vehicle requiring premium you risk detonation (knock). The vehicles performance and tuning baseline assumes 91/93 octane and when you mash the gas, if that level of anti-knock index is not available then detonation can occur. Yes today's ECU's are smart enough to detect and mitigate knock, but its a "reactive" measure not preventative. Meaning when detonation occurs it's already happen even though the ECU will immediate pull (retard) timing. Detonation is one of those things where it can happen repeatedly and have no affect, or happen once and destroy a motor. The most common damage from detonation is piston failure, either a ring/ringland or piston head.

Vehicle manufactures selling in the US must accommodate both levels of premium unleaded, as in some states only 91 is available. That said, all US vehicles requiring premium are actually tuned for 91 and not 93. Adding a higher octane fuel then required does nothing other then waste your money. The same is true with say a regular unleaded vehicle where the owner wants to add premium thinking there's some benefit or performance gain. The vehicles tuning will continue to perform the exact same assuming the proper type of fuel is being used. And in that example, the additional anti-knock capabilities from the higher octane go wasted and unused.

JeffK

I would add just two comments to your well thought out post:

1) The ECU is of course reactive not proactive. But I believe when the ECU detects knocking it reacts in mille seconds and thus prevents knocking.
2) As I posted, unless you are racing from a stop light, racing your car on the track or towing, the optimal potential horsepower is not used, thus there is no reason to use premium fuel.

Remember that by using premium, which because of its higher anti knock characteristics, a manufacturer can delay (retard) the spark, which results in higher potential horsepower.

As the ?Ultimate Driving Machine? BMW is in a horsepower race with its competition. Tuning an engine for premium vs. regular achieves approximately 7% more horsepower or about an additional 20 horsepower for the BMW 530i.

I own a 2010 528 i Xdrive with the 240 hp base six cylinder engine. I use this car for normal driving and ski trips ? often in the snow. Because I often drive in the snow, I opted for the lower horsepower engine in the 528i vs. 530i.

For my driving style (I do not gun the accelerator at a stop light, I am usually within 10% of the posted speed limit and the last time I was on a track (Lime Rock) was over 20 years ago) 223 HP (using regular) vs. 240 using premium is the same for me.

As I have absolutely no need for the additional 17 HP that premium would give me over regular, I prefer to use regular and put at the end of 4 years, the savings of $1,000 towards a vacation.

JeffK

pjinca

I'll just keep using Premium as the old addage goes: "an ounce of prevention is worth a pound of cure". On the of chance that detonation does happen and cause the above stated side effects (which is true), then better safe than sorry. Kind of hard to go on vacation knowing there's a $16k engine rebuild waiting for you.

vkhong

The next time you are trying to merge onto the highway safely between two trucks, get around a car on a two-lane road quickly and safely, or accelerate out of a tight spot to avoid getting boxed-in on the highway, tell me you won't miss that 17 HP Power and winter tires (during winter) are not needed 100% of the time. But during the split second when you need that extra power or extra traction - that's when they pay off. Power is not only for the track, it can be a savior in dangerous situations.I don't drive aggressively. On a 1400-mile road trip, I netted a moving average of 64 mph and 29 mpg. Yes, I did tap into the power reserve a few times in my E60 530i. The power was appreciated during the mountainous portion of the Interstate highway at 3000 ft above sea-level.

xcntrk

No offense, but some of you guys are way off here.

Premium fuel doesn't give you any more power then regular fuel without tuning for it. So this 17hp figure is snake oil. Your vehicle ECU and performance tuning are going to instruct the motor to perform at the same level with premium fuel as it would with regular fuel. Your vehicle has no way to identify what octane is present other than the clear instruction to the operator to use premium when filling. The only difference is without the detonation protection of 91/93 octane, which the ECU/motor is assuming exists and was tuned specifically to support, the motor will experience detonation as it tries to reach a performance level that the lower octane fuel cannot support.

Also knock detection is not really proactive. Vehicles have "knock sensors" which listen for the sound of detonation. When the ECU "hears" knock (aka knocking sound) it takes action to prevent any further knock. Meaning the initial detonation has already occurred and brief action has been taken to prevent any further det.

Lastly, you can make a vehicle run whatever fuel you want by modifying the performance tuning. Fuels with higher octane and therefore knock protection, allow the tuning to push more aggressively without detonating and therefore produce more power. Same is true with the opposite, you can add 87 octane as long as you're tuned for it (i.e. reduction in performance to account for lower octane and greater chances of knock). But the key here is that you must be tuned for the proper fuel. Simply adding it to the tank does not equal changes in performance. If you run out and buy C16 (116 octane race gas) and throw it in the tank, you're still going to produce the exact same amount of power that you did with 93 octane premium because your ECU is not "tuned" to take advantage of the high-performing fuel.

2exclusive

ok guys great info....sooooo your saying our cars should only be taking 91 octane and 93 is a waste of money unless we tune the ECU?

JeffK

In my prior post I indicated to achieve greater power you retarded the spark.

That is incorrect.

The opposite is true: With higher octane you can advance, not retard, the spark to achieve greater horsepower.

JeffK